A note on the avulsion of ranga river,district north Lakhimpur,Assam     

Suresh Chopra 《Journal of the Indian Society of Remote Sensing》1980,8(2):59-61

Ranga river, a major tributary of the Subanslri on the north bank of Brahmaputra exhibits the phenomenon of avulsion which has occured in the recent past. Avulsion has resulted primarily due to the building up of an alluvial ridge to the east.  相似文献   

Two-dimensional dynamic analysis of concrete gravity and embankment dams including hydrodynamic effects     

John F. Hall  Anil K. Chopra 《地震工程与结构动力学》1982,10(2):305-332

An analysis procedure in the frequency domain is developed for determining the earthquake response of two-dimensional concrete gravity and embankment dams including hydrodynamic effects; responses of the elastic dams and compressible water are assumed linear. The dam and fluid domain are treated as substructures and modelled with finite elements. The only geometric restriction is that an infinite fluid domain must maintain a constant depth beyond some point in the upstream direction. For such an infinite uniform region, a finite element discretization over the depth is combined with a continuum representation in the upstream direction. The fluid domain model approximately accounts for interaction between the fluid and underlying foundation medium through a damping boundary condition applied along the reservoir bottom, while the dam foundation is assumed rigid. Several examples are presented to demonstrate the accuracy of the fluid domain model and to illustrate dam responses obtained from the analysis procedure.  相似文献   

Hydrodynamic effects in dynamic response of simple arch dams     

Craig S. Porter  Anil K. Chopra 《地震工程与结构动力学》1982,10(3):417-431

The dynamic responses of simple arch dams, with different radius to height ratios are analysed for three conditions: the dam alone without water, and the dam with full reservoir, considering water to be compressible in one case and neglecting water compressibility in the other case. The complex frequency response functions for accelerations at the dam crest due to the three components of ground motion—upstream-downstream component, cross-stream component and vertical component–are presented. Based on these results, the effects of dam-water interaction, of water compressibility, and of bank motions on dam response are investigated.  相似文献   

A substructure method for earthquake analysis of structures including structure-soil interaction     

Jorge A. Gutierrez  Anil K. Chopra 《地震工程与结构动力学》1978,6(1):51-69

A general substructure method for analysis of response of structures to earthquake ground motion, including the effects of structure-soil interaction, is presented. The method is applicable to complex structures idealized as finite element systems and the soil region treated as either a continuum, for example as a viscoelastic halfspace, or idealized as a finite element system. The halfspace idealization permits reliable analysis for sites where essentially similar soils extend to large depths and there is no rigid boundary such as soil-rock interface. For sites where layers of soft soil are underlain by rock at shallow depth, finite element idealization of the soil region is appropriate; in this case, the direct and substructure methods would lead to equivalent results but the latter provides the better alternative. Treating the free field motion directly as the earthquake input in the substructure method eliminates the deconvolution calculations and the related assumption—regarding type and direction of earthquake waves—required in the direct method. Spatial variations in the input motion along the structure-soil interface of embedded structures or along the base of long surface supported structures are included in the formulation. The substructure method is computationally efficient because the two substructures—the structure and the soil region—are analysed separately; and, more important, it permits taking advantage of the important feature that response to earthquake ground motion is essentially contained in the lower few natural modes of vibration of the structure on fixed base.  相似文献   

Dynamics of towers surrounded by water     

C-Y. Liaw  Anil K. Chopra 《地震工程与结构动力学》1974,3(1):33-49

The effects of interaction with surrounding water on the dynamic response behaviour of cantilever tower structures are studied. Expressions for response to harmonic ground motion in individual modes of vibration, including hydrodynamic interaction, are presented, the accuracy of responses obtained by ignoring surface waves and compressibility of water in the hydrodynamic solutions is evaluated, the effects of hydrodynamic interaction on the fundamental period of vibration are studied and the commonly used ‘added mass’ approach to account for effects of surrounding water is examined. The conclusions deduced from the results of this investigation include the following. Interaction with surrounding water increases the fundamental period of vibration of the tower and decreases the modal damping ratio. Compressibility of water has essentially no influence in the hydrodynamic effects on slender towers. The traditional definition of added mass is conceptually deficient, but is simple to employ; the errors in this simple added mass representation are negligible for the first mode of vibration of towers.  相似文献   

Mathematical models for the dynamic analysis of concrete gravity dams     

Dixon Rea  C-Y. Liaw  Anil K. Chopra 《地震工程与结构动力学》1974,3(3):249-258

The results from field tests on Pine Flat Dam near Fresno, California, are described. The results are then used in the formulation of a three-dimensional mathematical model of the dam and a two-dimensional mathematical model of one of the taller monoliths. The significance of these mathematical models in relationship to the behaviour of concrete gravity dams during earthquakes is also discussed.  相似文献   

Letter to the editor discussion on paper     

A. K. Chopra  J. A. Gutierrez  T. H. Lee  D. A. Wesley 《地震工程与结构动力学》1974,3(4):401-401

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Earthquake resistance of buildings with a ‘soft’ first storey     

A. K. Chopra  D. P. Clough  R. W. Clough 《地震工程与结构动力学》1972,1(4):347-355

The dynamic, bi-linear response behaviour of a series of eight storey shear buildings subjected to simulated earthquake excitation is studied. The specific objective of the investigation is to determine under what conditions a yielding first storey can adequately protect the upper storeys from significant yielding. Two classes of buildings are considered: stiff (0.5 sec period) and flexible (2.0 sec period), and the basic parameters considered in the yielding first storey are the yield force level and the bi-linear stiffness. The results demonstrate that a very low yield force level and an essentially perfectly plastic yielding mechanism are required in the first storey to provide effective protection to the superstructure. Moreover, the required displacement capacity of such an effective first storey mechanism is found to be very large.  相似文献   

Estimation of seismic demands on isolators in asymmetric buildings using non‐linear analysis     

Keri L. Ryan  Anil K. Chopra 《地震工程与结构动力学》2004,33(3):395-418

A procedure based on rigorous non‐linear analysis is presented that estimates the peak deformation among all isolators in an asymmetric building due to strong ground motion. The governing equations are reduced to a form such that the median normalized deformation due to an ensemble of ground motions with given corner period T_d depends primarily on four global parameters of the isolation system: the isolation period T_b, the normalized strength η, the torsional‐to‐lateral frequency ratio Ω_θ, and the normalized stiffness eccentricity e_b/r. The median ratio of the deformations of the asymmetric and corresponding symmetric systems is shown to depend only weakly on T_b, η, and Ω_θ, but increases with e_b/r. The equation developed to estimate the largest ratio among all isolators depends only on the stiffness eccentricity and the distance from the center of mass to the outlying isolator. This equation, multiplied by an earlier equation for the deformation of the corresponding symmetric system, provides a design equation to estimate the deformations of asymmetric systems. This design equation conservatively estimates the peak deformation among all isolators, but is generally within 10% of the ‘exact’ value. Relative to the non‐linear procedure presented, the peak isolator deformation is shown to be significantly underestimated by the U.S. building code procedures. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

An improved capacity spectrum method for ATC‐40 by Y.‐Y. Lin and K.‐C. Chang,Earthquake Engineering and Structural Dynamics 2003; 32(13):2013–2026     

Anil K. Chopra 《地震工程与结构动力学》2005,34(1):97-97

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